1. Field of the Invention
The present invention relates to a data reader and a positioning system, and more specifically to a data reader for reading data from a storage medium from which data can be read by radio waves such as a RFID tag, a radio IC tag, etc., and positioning system using the data reader.
2. Description of the Prior Art
With the development of the recent radio communication technology and information processing technology, the management of articles by storing various kinds of information in a storage medium called a radio IC tag, and reading the information by radio waves has been developed. As an example of the technology, a data read system for management of hooks by assigning an IC tag storing the name or the code of a book to a book in a library, and reading it by a reader mounted near a bookshelf is disclosed in, for example, Japanese Patent Laid-Open No. 10-334198.
In the above-mentioned data read system, there can be the case where it is difficult or impossible to read data in its environment even in the range of the radio waves for a read that are radiated by a reader depending on the area or the position because reflected wave as radio waves for a read reflected by a wall, an article, etc. and direct waves of the radio waves for a read indicate inverse phases and interfere with one another in a certain point. In a point where the interference occurs, a radio IC tag cannot receive radio waves for a read from a reader. As a result, a data read from the radio IC tag fails.
When a plurality of readers and a plurality of antennas for readers are provided, the radio waves for a read radiated from each antenna interfere with one another, and in a point where the above-mentioned interference occurs, a data read from a radio IC tag fails.
The advantage of the present invention is to provide a data reader capable of changing an occurrence position of a dead spot (null point) as a point/area where it is difficult or impossible to read data due to the interference of radio waves for a read radiated from a data reader, and reading data regardless of a position of a radio IC tag.